Battery temperature greatly affects the performance, safety, and life of Li-Ion batteries in hybrid vehicles under various driving conditions. As a result, automakers and battery suppliers are paying increased attention to thermal management for Li-Ion batteries. Driving conditions and the type of heating and cooling can create an uneven temperature distribution in a battery pack. This uneven temperature distribution can lead to electrically unbalanced modules, and thus to lower performance and shorter battery life. Battery thermal management systems play a significant role in Hybrid Electric Vehicle (HEV) applications by addressing the Li-Ion battery thermal safety, in addition to improving performance and extending the battery cycle life.
The magnitude of the battery heat generation rate from the modules in a battery pack affects the size and design of the battery thermal management system. Battery heat generation depends on the magnitude of the cell internal resistance and the thermodynamic heat of the electrochemical reaction. Thus, the heat generation rate depends on the discharge/charge profile and the cell's state of charge and temperature. In order to achieve optimum performance from a battery, it is desirable to operate the battery in a desired temperature range and to reduce uneven temperature distribution.
Poor thermal management can lead to a reduction in battery performance, and thus to a substantial increase in cost, reduced cycle and calendar life, and an increased chance of abuse conditions. One current approach to battery cooling uses indirect liquid cooling. However, these systems are heavy, and costly, and they have potential quality problems associated with leakage. Another current approach uses air cooling. However, these systems do not have sufficient cooling capacity, and they require a large air flow rate, which introduces noise and vibration problems in the cooling system. Consequently, air cooling systems provide a limited cooling performance. However, a thermal management system using air as the heat transfer medium is less complicated than a system using liquid for cooling/heating.